Cell Growth & Division
I. Growth
A. Growth is defined as the increase in
volume of the protoplasm as well as the
increase in the number of individual cells.
The increase in volume comes about by the
assimilation of food materials into living
material within the cell itself.
B. Because of this increase within, the
cytoplasm (volume) of the cell increases
more rapidly than the plasma membrane
(surface area).
C. The information that controls a cell is stored
inside the nucleus.
This is the material we call DNA located within
the chromatin material.
As the cell gets larger, the information has a
harder time controlling the increasing
cytoplasm.
Eventually, there comes a point where the cell
can not grow any larger.
Cell Size
Surface Area
(length x width x 6)
Volume
(length x width x height)
Ratio of Surface Area
to Volume
D. Since cells depend on the amount of food
and oxygen they can absorb through their
plasma membranes (surface area), the
continued growth of the cell becomes
impossible.
At the same time, the cell will not be able to rid
itself of its own waste products which also must
leave through the plasma membrane.
E.
For these two main reasons the
cell is faced with one of 3 possibilities:
1. die
2 stop growing, or
3. divide.
4. The first is not a real choice at all, cells are
going to survive if at all possible.
Some cells actually do stop growing, our nerve
tissue follows this path.
Nerve tissue does not have the ability to
undergo mitosis. You are essentially born with
all of the nerve cells you are ever going to have
for the rest of your life.
Any nerve tissue which is injured or damaged
will not be replaced with new cells.
Most of our cells however, in order to survive,
must divide and restore the balance between
the surface area and volume.
F.
Mitosis / Cell division –
Cell division results in the growth of the
body as a whole--this increases the total
number of cells in the body.
Mitosis is the name of the process cells
go through as they divide.
Most cells go through a cell cycle that
includes mitosis.
G. The cell cycle consists of 4 phases:
G1, S, G2 & M.
G1, S & G2 are also known as Interphase.
Interphase is the normal, functioning phase
and not one of active cell division, however it
should be noted that replication of DNA and
the duplication of the centrosome takes place
in interphase--both necessary before mitosis
can take place.
G1 phase
M phase
S phase
G2 phase
1.
G1 is the period when cells grow (1st growth). They
increase their (size) protoplasm and carry out their
activities. Some organelles are made as well.
2.
S is the synthesis phase. During this period, the DNA
material is replicated. This means that new DNA material
is made. It is an exact copy of the original DNA material
that is in the nucleus.
3.
G2 is the phase where final production of organelles
takes place (growth of parts, 2nd growth) and the cell
finishes preparations for cell division.
4.
M is the phase where mitosis takes place. It consists
of mitosis and cytokinesis. It results in two identical
daughter cells being produced.
a. Mitosis consists of 4 subphases:
1. prophase
2. metaphase
3. anaphase
4. telophase
b. Cytokinesis
1. This process occurs
during telophase.
2. The cytoplasm is divided by
the cell membrane.
a. Animal cells pinch inward
from the edges
b. Plant cells build a cell
plate between the cells.
1. INTERPHASE- not a stage of
division but the “normal” phase of life
for most cells.
a.
b.
c.
Grows (G1)
replicates DNA (S)
duplicates centrosome (G2)
d.
G2)
functions for the body (G1,S, &
e.
Includes phases G1,S & G2
Cell membrane
Cell during Interphase
Nuclear membrane
Chromatin material
Nucleolus
Centrosome
Replication of DNA during Interphase
Duplication of centriole during Interphase
centriole
centrosome
Mitosis:
1.
PROPHASE
a.
b.
c.
first stage of division
chromatin becomes condensed into chromosomes
nucleolus fades and disappears
d. the centrosome divides forming 2 daughter
centrioles. the daughter centrioles start moving toward
opposite ends of the cell. They are connected by lines of
granules, the spindle fibers, these start forming
between the centrioles.
e.
nuclear membrane fades and disappears
Replication of DNA during
Interphase
DNA condensing during
Prophase
centromere
Detailed structure of
one chromosome
genes
2 chromatids
PROPHASE DIAGRAM
Spindle fibers
2.
METAPHASE
a.
the chromosomes now are arranged
in the middle of the cell.
b. nuclear membrane, nucleolus are
gone
c.
spindle fibers are completely
formed and attached to the chromosomes
Metaphase diagram
3.
ANAPHASE
a.
the spindle fibers now begin to
draw apart each chromatid member of a
chromosome to opposite ends of the cell.
In this manner a precise division of the
chromatin material is brought about.
This is known as karyokinesis.
b. the plasma membrane now begins to
pinch inwards.
Anaphase diagram
Karyokinesis occurs
Cell membrane
pinching inward
(animal cells)
Cell plate developing
(plant cells)
Anaphase diagram
Plant cells also lack
centrioles
4.
TELOPHASE
a.
once the chromatids have reached
opposite ends of the cell, the reverse of
prophase occurs.
b. nuclear membrane and nucleolus
reform,
c.
the chromotids become chromatin
d. there is one centriole in each new
cell
4.
TELOPHASE
e. interphase is resumed as soon as the
cytoplasm completely separates (cytokinesis),
forming 2 new daughter cells.
f.
Mitosis produces an exact copy of the
original parent cell. The DNA material is
replicated in Interphase, giving the parent cell 2
complete and identical sets of DNA information.
This material is divided into 2 new daughter cells,
each receiving one complete set of DNA
information from the original parent cell.
Cytokinesis is completed
Telophase diagram
Mitosis produces identical cells with the same DNA.
46
46
46
Section 10-2
Spindle
forming
Centrioles
Nuclear
envelope
Chromatin
Centromere
Chromosomes
(paired chromatids)
Interphase
Prophase
Cytokinesis
Go to
Section:
Spindle
Centriole
Telophase
Nuclear
envelope
reforming
Centriole
Individual
chromosomes
Anaphase
Metaphase
Section 10-2
Spindle
forming
Centrioles
Nuclear
envelope
Chromatin
Centromere
Chromosomes
(paired chromatids)
Interphase
Prophase
Cytokinesis
Go to
Section:
Spindle
Centriole
Telophase
Nuclear
envelope
reforming
Centriole
Individual
chromosomes
Anaphase
Metaphase
Section 10-2
Spindle
forming
Centrioles
Nuclear
envelope
Chromatin
Centromere
Chromosomes
(paired chromatids)
Interphase
Prophase
Cytokinesis
Go to
Section:
Spindle
Centriole
Telophase
Nuclear
envelope
reforming
Centriole
Individual
chromosomes
Anaphase
Metaphase
Section 10-2
Spindle
forming
Centrioles
Nuclear
envelope
Chromatin
Centromere
Chromosomes
(paired chromatids)
Interphase
Prophase
Spindle
Cytokinesis
Centriole
Telophase
Nuclear
envelope
reforming
Go to
Section:
Centriole
Individual chromatids
Metaphase
Anaphase
Karyokinesi
s
Section 10-2
Spindle
forming
Centrioles
Nuclear
envelope
Chromatin
Centromere
Chromosomes
(paired chromatids)
Interphase
Prophase
Cytokinesis
Go to
Section:
Spindle
Centriole
Telophase
Nuclear
envelope
reforming
Centriole
Individual
chromosomes
Anaphase
Metaphase
Section 10-2
Spindle
forming
Centrioles
Nuclear
envelope
Chromatin
Centromere
Chromosomes
(paired chromatids)
Interphase
Prophase
Cytokinesis
Go to
Section:
Spindle
Centriole
Telophase
Nuclear
envelope
reforming
Centriole
Individual
chromosomes
Anaphase
Metaphase
Section 10-2
Spindle
forming
Centrioles
Nuclear
envelope
Chromatin
Centromere
Chromosomes
(paired chromatids)
Interphase
Prophase
Cytokinesis
Go to
Section:
Spindle
Centriole
Telophase
Nuclear
envelope
reforming
Centriole
Individual
chromosomes
Anaphase
Metaphase
A. Reproduction is the ability to produce
another individual organism of the same
type. This process is necessary for the
continuation of any species. Man is a
complex organism in which specialization of
certain cells has developed for this purpose.
Special cells are produced which contain the
necessary genetic material. Humans (which
reproduce sexually) require that that 2
individuals be involved in this process.
In this way, each parent furnishes 1/2 the
genetic material. This produces new genetic
combinations in the offspring making each
individual totally unique. It is this
uniqueness that gives a survival edge to
some individuals in a changing environment.
B. Meiosis– Reproduction requires a more
sophisticated and complex type of cell
division than mitosis. It is called
meiosis. This a special type of cell
division that results in a reduction of
the number of chromosomes in a cell.
The process is used to produce gametes
(sex cells) for sexual reproduction.
a. Meiosis consists of 8 phases in 2 series of division.
(1) Series 1
(a) Prophase I
(b) Metaphase I
(c) Anaphase I
(d) Telophase I.
(2) Series II
(a) Prophase II
(b) Metaphase II
(c) Anaphase II
(d) Telophase II
Separated by a short interkinesis
(interphase-like phase) to replace
ATP and duplicate the centrioles in
each cell
1.
P
Sexual Reproduction:
♂
46 (2 sets)
♀
46 (2 sets) diploid number (2N)
(somatic cells)
-------------------- -MEIOSIS- --------------------------sperm
egg
haploid number (1N)
(germ cells) gametes
23 (1 set)
F1
46
2 sets (2N)
zygote
23 (1 set)
sex cells
zygote
first cell of the new
individual
diploid somatic cells
2.
In the nucleus of cells, the DNA
information is in 2 complete sets, (one
from Dad and one from Mom).
In meiosis the DNA information is divided
into 2 sets of information, reducing the
number of chromosomes from 46 to 23. In
prophase I, the process of synapses is of
great importance, since it is here that the
homologous chromosomes (tetrad) pair up to
achieve the separation of the 2 sets of DNA
information in later stages.
Cell membrane
Cell at the end of Interphase
Nuclear
membrane
Chromatin material
(replicated DNA)
Nucleolus
Centrosome
Prophase I
a.
chromatin becomes condensed into
chromosomes
b.
synapses occurs
c.
nucleolus fades and disappears
Prophase I
d.
the centrosome divides forming 2
daughter centrioles. the daughter
centrioles start moving toward opposite
ends of the cell. They are connected by
lines of granules, the spindle fibers, these
start forming between the centrioles.
e.
nuclear membrane fades and
disappears
Synapses- the pairing up of homologous chromosomes.
homologous chromosomes- chromosomes that contain
information for the same traits, “alike” chromosomes
hair color
(black)
# of toes
curly/
straight
hair
A
B
type of
nose
hair color
..
..
(blond)
color of eyes
(brown)
# of toes
type of nose
freckles/
curly/
straight hair no freckles
freckles/
no freckles
# of fingers
color of eyes
(blue)
C
D
# of fingers
Gene maps- a drawing showing the relative locations
of each known gene on the chromosomes.
Tetrads and Crossing Over
Brown
eyes
blue eyes
no
Freckles
Freckles
6 fingers
5 fingers
Homologous
chromosome pair
moving into tetrad
position
tetrad position; 4
chromatids of homologous
chromosomes
Brown
eyes
Crossing
over
no
Freckles
blue eyes
blue eyes
Freckles
no freckles 6 fingers
Freckles
5 fingers
Brown
eyes
6 fingers
5 fingers
crossing over between
chromatids (DNA exchanged)
Resulting chromosomes: a new
combination of genetic material has
been formed by the exchange.
Gene linkage causes some traits to be inherited together
most of the time; however, crossing over can change
linkage.
Brown
eyes
No
Freckles
5 fingers
Brown
eyes
No
Freckles
6 fingers
blue eyes
blue eyes
Freckles
6 fingers
Freckles
5 fingers
Gene Linkage & Crossing Over
Brown
eyes
Brown
eyes
no
Freckles
no
Freckles
5 fingers
6 fingers
blue eyes
blue eyes
Freckles
Freckles
6 fingers
5 fingers
Now, there exists 4 different chromatids.
2 of these combinations didn’t exist
before crossing over took place. The
gametes produced from these 4 different
combinations will produce different
gametes with different information.
To follow this
change we will
color code our
chromosomes
and their new
exchanged DNA
PROPHASE I DIAGRAM
Chromosome pair
METAPHASE I
a. nuclear membrane, nucleolus are
gone
b.
spindle fibers are completely
formed and attached to the chromosomes
c.
the chromosome pairs are now
arranged in the middle of the cell.
d. Random chance determines the
independent assortment that results
from the chromosome pairs lining up
along the middle of the spindle fibers.
Metaphase I diagram
A B
CD
Metaphase I diagram
A B
DC
ANAPHASE I
a.
the spindle fibers now begin to draw each
chromosome of the chromosome pair to opposite ends
of the cell.
•In this manner a precise division of the chromatin
material is brought about.
•½ of the information contained on each
chromosome pair is separated.
•One set of information will move to the opposite
ends of the cells.
•This is the separation or segregation of the genetic
pairs of information.
•This is a special type of karyokinesis.
ANAPHASE I
b. the plasma membrane now begins to
pinch inwards (animal cells) or develop a
cell plate (plant cells).
Anaphase I diagram
A
B
D
C
TELOPHASE I
a.
once the chromosomes have reached
opposite ends of the cell, the reverse of
prophase I occurs.
b. nuclear membrane and nucleolus reform,
c. the chromosomes become chromatin
d.
there is one centriole in each new cell
e. This 1st stage of meiosis has divided the 2
sets of information into 2 separate cells with 1
set of information in each.
Telophase I diagram
A D
B C
The cells now go into interkinesis. This is
a short period like interphase. During
this phase the cell will restore its ATP and
the centrosome will be duplicated for the
next series of phases.
2nd series begins:
PROPHASE II
a. chromatin becomes condensed into
chromosomes
b.
nucleolus fades and disappears
2nd series begins:
PROPHASE II
c. the centrosome divides forming 2
daughter centrioles. the daughter centrioles
start moving toward opposite ends of the cell.
They are connected by lines of granules, the
spindle fibers, these start forming between
the centrioles.
d.
nuclear membrane fades and
disappears
PROPHASE II DIAGRAM
A D
B C
METAPHASE II
a.
the chromosomes now are arranged in
the middle of the cell.
b.
nuclear membrane, nucleolus are gone
c.
spindle fibers are completely
formed and attached to the chromosomes
d. The centrioles always change their
orientation each time they undergo a new
division. They re-orientate 900 to their last
position.
Metaphase II diagram
A D
B C
ANAPHASE II
a.
the spindle fibers now begin to
draw each chromatid member of a
chromosome to opposite ends of the cell.
In this manner a precise division of the
chromatin material is brought about.
This is known as karyokinesis.
b. the plasma membrane now begins to
pinch inwards or build a cell plate.
Anaphase II diagram
A D
B C
TELOPHASE II
a.
once the chromatids have reached
opposite ends of the cell, the reverse of
prophase occurs.
b. nuclear membrane and nucleolus
reform,
c.
the chromatids become chromatin
d. there is one centriole in each new cell
e. interphase is resumed as soon as the
cytokinesis is completed.
TELOPHASE II
f.
Meiosis has produced 4 cells, each
with ½ the original genetic information.
These cells are haploid or 1N. This refers
to the fact that they have 1 set of genetic
information. These cells are not alike and
will form different gametes.
g. These cells will continue to
modify and become sex cells.
Telophase II diagram
A D
B C`
A D`
B C
4 haploid (1N) cells are produced that are each
carrying different genetic information.
In the male, all will become sperm.
In the female, 3 will die off and 1 will remain as the egg.